1. Field of the Invention
The present invention relates to a two-group zoom projection lens to be mounted on a projection display and to such a projection display. Particularly, the present invention can be used as a projection lens for use on a projector that employs a DMD (digital micro-mirror device) for its light valve.
2. Description of Background Art
Recently, the projectors (projection displays) using DMD displays have becoming popular in addition to liquid crystal displays. The DMD uses highly-reflective rectangular microscopic mirrors capable of tilting in the range of some 10 degrees or more, to control the reflective direction of the light from the light source in accordance with an input video signal and to focus only a desired portion of reflection light onto a screen thereby projecting the video image. This can be effected by digitally controlling, quite independently, the several millions or more mirrors arranged two-dimensionally on a substrate. Each mirror corresponds to one pixel in a video image.
Meanwhile, differently from the liquid crystal display, the DMD is low in light loss because of no need to polarize illumination light, and hence excellent in the correctness of continuous-tone representation. The projector using such an advantageous DMD requires a projection lens having a favorable lens characteristic in order to obtain a clear high-definition projection image in accordance with the DMD. In an attempt to meet the requests, there is proposed a projection lens capable of making a correction for aberrations at a wide angle-of-view (see JP-A-2004-271668).
For a projector using a DMD, the projection lens is necessarily matched to the characteristic and requirement of the projector. Accordingly, the first requirement is for high performance and small size. Furthermore, naturally required is suitability in correction, at wide angle-of-view, for aberrations, including chromatic aberration and distortion. In the recent that high-definition color images are particularly needed, required are those that are favorable in chromatic aberration.